1. Field of the Invention
The present invention relates to an image forming system for forming an image on a recording material. Specifically, the present invention relates to an image forming system for obtaining an output with a smooth surface using a recording material having a surface provided with a toner receiving layer composed of a thermoplastic resin.
The image forming system can be used for, for example, a copying machine, a printer, and FAX, which form images by an electrophotographic system, and a compound machine having the functions of these apparatuses.
2. Description of the Related Art
Many image forming apparatuses for forming full-color images have been commercialized and requirements for image quality have been increasingly advanced with use in various fields.
In particular, in order to improve the quality of full-color images, it is required to improve image glossiness. One of factors which determine the glossiness of images is the smoothness of output images.
For such a requirement, Japanese Patent Laid-Open Nos. 2004-205563 and 2006-250979 have proposed an image forming apparatus for forming a color image using a recording material provided with a transparent resin layer (toner receiving layer) composed of a thermoplastic resin. In this image forming apparatus, a toner image is fixed to the transparent resin layer using a first fixing device not provided with a cooling device and then smoothed by a second fixing device provided with a cooling device.
Specifically, in the first fixing device, heating and pressing are performed in a degree which allows the toner to be temporarily fixed to the transparent resin layer. This is aimed at preventing offset of the toner to another conveying mechanism in a process of conveying a recording material to the second fixing device.
On the other hand, in the second fixing device, the recording material on which the toner image has been fixed is pressed and heated with a high-gloss belt and then cooled while being adhered to the belt. After the recording material is sufficiently cooled, the recording material is separated from the belt.
As a result, the toner image is buried in the transparent resin layer of the recording material, and the transparent resin layer is smoothed by the surface of the belt, thereby forming a color image with excellent glossiness. Therefore, such an image forming technique attracts attention because it can produce an output with high glossiness equivalent to a silver-salt photograph in spite of being an electrophotographic image forming apparatus.
However, the configurations disclosed in Japanese Patent Laid-Open Nos. 2004-205563 and 2006-250979 may cause the problem described below.
Specifically, in spite of heating and pressing treatment in a degree which allows the toner to be temporarily fixed to the transparent resin layer, there may be caused the phenomenon that the recording material cannot be properly separated from the first fixing device due to the transparent resin layer on the surface of the recording material.
This is possibly due to the fact that the transparent resin layer functions as an adhesive because the leading region of the recording material in the conveyance direction is a region (so-called margin) in which the toner image is not formed, and the recording material at a high temperature is separated from the first fixing device.
In particular, the problem is significant when a resin not containing a wax component is used in the transparent resin layer of the recording material in view of compatibility with the toner. This is because the releasing effect of the wax component cannot be expected.
When the thickness of the recording material is increased for preventing defective separation, a large quantity of energy is required for the heating and cooling steps. Therefore, this method is not a measure for resolving the problem.